1. Field of the Invention
The present invention relates to a high-purity alkali etching solution for silicon wafers and a method for etching silicon wafers using the solution.
2. Background Art
In producing silicon wafers for use, e.g. in integrated circuits such as an IC or an LSI and for manufacturing individual semiconductor devices such as transistors and diodes, silicon wafers are generally manufactured by cutting a single crystal obtained by the Czochralski method (CZ method) or by the Floating Zone method (FZ method) with an inner blade saw or a wire saw, chamfer processing the periphery, lap processing at least one surface with free abrasives to improve the surface flatness, followed by wet etching the wafer to eliminate processing distortion introduced during these processes; and then mirror polishing the wafer. One type of wet etching which has been employed to eliminate process distortion is alkali etching using an alkali such as sodium hydroxide or potassium hydroxide. Such alkali etching has the advantage of obtaining good surface flatness of the wafer after etching, since the alkali etching rate is slow, but has the disadvantage of diffusing metal impurities included in the alkali etching solution into the wafer during the etching process.